Direct current power transmission system



Feb. 7, 1939. Q w U T 2,146,571

DIRECT CURRENT POWER TRANSMISSION SYSTEM Filed Aug. 1, 1938 lo 26 A25 Inventor wolFgan b Gunther, by Z His Attorney.

Patented Feb. 7, 1939 UNITED STATES PATENT OFFICE Wolfgang Giinther, Siemensstadt, Germany, assignor to General Eiectric Company, a corporation of New York Application August 1, 1938, Serial No. 222,479 In Germany June 1, 1937 Claims.

My invention relates to direct current power transmission systems and more particularly to such systemsutilizing electric valve translating apparatus at the transmitting and receiving ends.

In direct currentpower transmission systems utilizing electric valve translating apparatus at thetransmitting and receiving ends it has been found difiicult to place the transmission system into operation wheresuch systems are not pro- 19 vided with a neutral wire, and more particularly in such systems where the electric valve translating apparatus utilizes electric arc discharge valves of the type described in a book by Erwin Marx entitled Lichtbogenstromrichter published in Berlin in 1932,.and in United States Letters Patent No, 2,074,930, granted March 23, 1937, upon the application of Erwin Marx. Valves of the latter system utilize a pair of main electrodes and an auxiliary or starting electrode. In this latter type of valve the ignition impulse is generally very short and hence it is difficult to render conductive all of the valves at the same time. The same difiiculty also occurs where electric valves of the usual gaseous type are utilized with a con trol or ignition impulse of short duration. Once the proper number of electric valves has been rendered conductive in each of the translating apparatus the transmission system will continue to function in its normal manner.

It has been suggested heretofore that a direct current neutral wire be utilized to interconnect the neutral points of the network in each of the translating systems in order to obviate the difficulties of starting the transmission system, but when this wire is added it has the disadvantage of introducing a predominant direct current ripple of the fundamental frequency. Since this is undesirable some other means should be provided to facilitate the starting of the transmission system and preferably such means must have relatively no eifect upon the transmission system once it has started. In accordance with my invention a starting impedance or resistance is connected between the neutral points of the inductive net- 45 L work of the electric valve translation system and the ground so that this impedance cooperates with the line-to-ground capacitance of the transmis sion system to produce a leakage path capable 50 of carrying a current just sufficient to permit the necessary number of valves in each translating system to become conductive. Preferably such leakage path should have a relatively high impedance value after thetransmission system has 55 been started and this is accomplished in accordunderstood by reference to the following descripance with my invention by providing an impedance circuit having a nonlinear resistance-current characteristic. This may be accomplished in any one of several Ways such as utilizing the combination of a resistor and a nonlinear or saturable re- 5 actor or by utilizing a resistance element having a nonlinear resistance current characteristic.

It is, therefore, an object of my invention to provide a transmission system utilizing electric valve translating or converting apparatus which will overcome certain limitations of the arrangements of the prior art, and which will be simple and reliable in operation.

It is another object of my invention to provide an arrangement for facilitating the starting of 5 the electric valve translating apparatus in a direct current transmission system which arrangement will have substantially no effect on the transmission system after normal operation has been initiated.

Still another object of my invention is to provide during the starting operation of the transmission system an auxiliary or leakage path sufficient to transmit the current necessary for starting the valves and for providing effectively an impedance between the valve apparatus and the ground such that normal operation of the system is not materially affected thereby.

The novel features which I believe to be characteristicof my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, will be better tion taken in connection with the accompanying drawing in which the single figure shows a direct current transmission system utilizing a plurality of electric valve translating apparatus to which my invention has been applied. 40

Referring now more particularly to the single figure of the drawing, there is disclosed an arrangement embodying my invention for transmitting energy from the alternating current sup- I ply circuit It] to the alternating current load circuit l, by means of an electric valve translating apparatus I 2, a direct current transmission line 83, and an electric Valve translating apparatus M. The translating apparatus l2 includes a transformer having a primary winding l5 connected to the alternating current supply circuit [0, and a secondary winding l6 which is preferably arranged in star relation so as to provide a neutral point. The other extremities of the secondary winding l6 are'each connected to both sides of the direct current transmission line I3 by means of a plurality of serially connected pairs of valves I1, I8; I9, 20; and 2!, 22. While for the purposes of illustration I have shown each of the valves Ii to 22 as comprising an anode, a cathode and a control electrode enclosed within an envelope containing an ionizable medium, the valves may be any of the types commonly known in the art including those of the type described by Erwin Marx in the above identified references. The anodes of the valves I'I, I9 and 2| are each connected through a suitable smoothing reactor 23 to one side of the direct current transmission line I3 and the cathodes of these valves are respectively connected to the anodes of the valves I8, 25 and 22. All of the cathodes of the valves I8, 26 and 22 are connected through a suitable smoothing reactor 24 to the other side of the direct current transmission line I3. The electric valve translating apparatus I4 includes a transformerihaving an output winding 25 connected to the alternating current load circuit II and an input winding 26 which is arranged so as to have a neutral point, and the outer extremities thereof are interconnected with the direct current transmission line by means of a plurality of pairs of valves 21, 28; 29, 30; and 3!, 32 through a pair of smoothing reactors 33 and 34. In accordance with my invention the electric valve translating apparatus M is provided with a connection between the neutral point of the transformer winding 26 and the ground which includes a suitable reactor 35 and if necessary a resistor 36 which will operate to properly damp any oscillation tendency. The inductor 35 under normal operating conditions of the transmission system is slightly saturated and during the time that the transmission system is starting up this coil is over-saturated. Thus the impedance of the circuit comprising the inductor 35 and the resistor 3t is relatively small during the starting of the transmission system and relatively high during normal operation. The electric valve translating system I2 is provided with a similar circuit arrange-mentor may be provided as shown with a resistance element 37 which has a nonlinear resistance current characteristic. Resistors of this type have ben shown, described and claimed in United States Letters Patent No. 1,822,742, granted September 8, 1931, upon the application of K. B. McEachron, for Discharge device and resistance material and which is assigned to the same assignee as the present application. Such resistance material comprises a granular substance having a hyperbolic resistance-ampere characteristic so that when applied between the neutral point of the transformer I6 and the ground there will be presented to the transmission system a relatively high impedance during normal operating conditions and during the starting conditions element 36 will present a relatively low impedance value to the transmission system. Thus, in accordance with my invention there is provided for each translating apparatus paratus I2 the resistor 31 which has a nonlinear resistance-current characteristic cooperates with capacitances 38 and 39 of the. direct current transmission line I3 to provide the necessary starting or leakage path for this apparatus.

Numerous conditions are contributory to the difl'iculties encountered in placing the transmission system into operation when it is not provided with the features of the present invention, or with a neutral conductor. One of these difficulties is encountered in attempting to obtain absolute synchronism of the moments at which two of the valves of the translating apparatus become conductive. In addition the moment of ignition of any pair of valves of the translating apparatus [4 is generally phase displaced with respect to the moment of ignition of a similar pair of valves in'the translating apparatus I2. Since during the starting operation leakage paths are provided in accordance with my invention, it will be apparent that like differences in the time at which the individual valves actually become conductive will not prevent the transmission system from being placed into operation. As soon as the proper number of valves are rendered conductive substantially all of the current is carried by the direct current transmission line I3 so that no current flows through the neutral connections of the translating apparatus and hence the circuit connected between these neutral points and the ground assumes a high impedance value.

While I have shown a particular application of my invention to an electric transmission system utilizing a plurality of electric valve translating apparatus, it will be understood that this is merely illustrative as one of a number of electric transmission systems and one of a number of electric valve translating apparatus to which my invention may be applied. It is to be understood that my invention provides during the starting operation of the valve apparatus a shunt or leakage path having a sufficient current carrying capacity to permit the proper valves to be rendered conductive and that during subsequent normal operation of the transmission system and the associated valve apparatus the circuits have such high impedance as to produce no substantial effect upon the transmission system.

While I have shown and described my invention in connection with a certain specific embodiment, it will, of course, beunderstood that I do not wish to be limited thereto, since it is apparent that the principles herein disclosed are susceptible of numerous other applications, and modifications may be made in the circuit arrangements to which my invention may be applied without departing from the spirit and scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination comprising a supply circuit, a load circuit, a plurality of electric valve translating apparatus and a transmission line interconnecting said circuits, each of said translating apparatus including an inductive network provided with a neutral point and a plurality'of pairs of electric arc discharge valves cannected in series across said transmission line, and an i impedance means for each network connected between the neutral points thereof and the ground, said impedances each having a nonlinear resistance-current characteristic and cooperating with the capacitance-to-ground of said transmission line to facilitate the starting of said translating apparatus.

2. The combination comprising an alternating current circuit, a direct current circuit having an appreciable capaoitance-to-ground, an electric valve translating apparatus interconnecting said circuit, said apparatus including an inductive network, provided with a neutral point and a plurality of pairs of serially connected electric arc discharge valves arranged across said direct current circuit, and an impedance means connected between the neutral point of said network and the ground, said impedance having a nonlinear resistance-current characteristic and cooperating with the capacitance-to-ground of said direct current circuit to facilitate the starting of said translating apparatus.

3. The combination comprising a supply circuit, a load circuit, a plurality of electric valve translating apparatus and a transmission line interconnecting said circuits, each of said translating apparatus comprising an inductive network provided with a neutral point and a pair of electric arc discharge valves interconnecting each terminal of said network with both sides of said transmission line, and means for facilitating the starting of the valves of said apparatus comprising a plurality of impedances each having a nonlinear resistance-current characteristic, said impedances each being connected between the ground and a neutral point of each inductive network.

4. The combination comprising a supply circuit, a load circuit, a plurality of electric valve translating apparatus and a transmission line interconnecting said circuits, each of said translating apparatus comprising an inductive network provided with a neutral point and a pair of electric arc discharge valves interconnecting each terminal of said network with both sides of said transmission line, and an impedance means for each network connected between the neutral point thereof and the ground, said impedances each having a nonlinear resistance-current characteristic and cooperating with the capacitanceto-ground of said transmission line to facilitate the starting of said translating apparatus.

5. The combination comprising an alternating current supply circuit, an alternating current load circuit, a plurality of electric valve translating apparatus and a direct current transmission line interconnecting said circuits, each of said translating apparatus comprising an inductive network provided with a neutral point and a pair of electric arc discharge valves interconnesting each terminal of said network with both sides of said transmission line, and an impedance means for each network connected between the neutral point thereof and the ground, said impedance means having a nonlinear resistancecurrent characteristic and cooperating with the capacitance-to-ground of said transmission line to facilitate the starting of the valves of said translating apparatus.

WOLFGANG GTL'TNTHER. 

